How to get the size of a spatial index?

I want to see the size of a spacial index. I am usually using one of the following code blocks to get the indexes sizes of a given table, but none of them is working for a spatial index.

DECLARE @DataSource TABLE
(
    [TableName] SYSNAME
   ,[IndexName] SYSNAME
);

INSERT INTO @DataSource ([TableName], [IndexName])
VALUES ('[dbo].[Table]', 'Index');

SELECT OBJECT_NAME(INX.[object_id]) AS TableName
      ,INX.[name] AS IndexName
      ,INX.[index_id] AS IndexID
      ,8 * SUM(AU.[used_pages]) AS 'Indexsize(KB)'
FROM [sys].[indexes] AS INX
INNER JOIN [sys].[partitions] AS PAR
    ON PAR.[object_id] = INX.[object_id] 
    AND PAR.[index_id] = INX.[index_id]
INNER JOIN [sys].[allocation_units] AS AU 
    ON AU.[container_id] = PAR.[partition_id]
INNER JOIN @DataSource DS
    ON INX.[object_id] = OBJECT_ID(DS.[TableName])
    AND INX.[name]  = DS.[IndexName]
GROUP BY INX.[object_id]
        ,INX.[index_id]
        ,INX.[name]
ORDER BY OBJECT_NAME(INX.[object_id])
        ,INX.[index_id]

OR

CREATE TABLE #CompressionResults
(
     [object_name] SYSNAME
    ,[schema_name] SYSNAME
    ,[index_id] INT
    ,[partition_number] INT
    ,[size_with_current_compression_setting (KB)] BIGINT
    ,[size_with_requested_compression_setting (KB)] BIGINT
    ,[sample_size_with_current_compression_setting (KB)] BIGINT
    ,[sample_size_with_requested_compression_setting (KB)] BIGINT
)

INSERT INTO #CompressionResults
EXEC sp_estimate_data_compression_savings 'dbo', 'A', NULL, NULL, 'ROW' ;

SELECT CR.[object_name]
      ,IDX.[name]
      ,[size_with_current_compression_setting (KB)] / 1024  AS [current size (MB)]
      ,[size_with_requested_compression_setting (KB)] / 1024  AS [size after compression (MB)]
      ,([size_with_current_compression_setting (KB)] - [size_with_requested_compression_setting (KB)]) / 1024 AS [saved size (MB)]
FROM #CompressionResults CR
INNER JOIN [sys].[indexes] IDX
    ON CR.[index_id] = IDX.[index_id]
    AND OBJECT_ID(CR.[object_name]) = IDX.[object_id]
UNION ALL
SELECT CR.[object_name]
      ,'ALL'
      ,SUM([size_with_current_compression_setting (KB)]) / 1024  AS [current size (MB)]
      ,SUM([size_with_requested_compression_setting (KB)]) / 1024  AS [size after compression (MB)]
      ,SUM([size_with_current_compression_setting (KB)] - [size_with_requested_compression_setting (KB)]) / 1024 AS [saved size (MB)]
FROM #CompressionResults CR
GROUP BY CR.[object_name]

DROP TABLE #CompressionResults